Technical Abstract:
Limited information is available on the effects of crop rotation, N fertilization, and tillage on soil organic C (SOC) sequestration under irrigated conditions. This study examined the influence of no-till (NT), irrigated crop rotations [continuous corn (C-C), barley-corn (B-C), soybean-corn (S-C)] and N fertilization (6 N levels) on SOC sequestration compared with conventional plow tillage (CT) continuous corn with 4 N levels. Quantity of crop residue C returned to the soil by each rotation was in the order C-C>B-C>S-C. After 3 crop years, SOC increases in the 0 to 15 cm depth were in the order C-C(NT)>B-C(NT)>S-C(NT)>C-C(CT). Application of N increased the level of residue C returned to soil in all systems, with trends of increasing SOC with N application in the NT systems. With increasing rate of N application, the C/N ratio of the residue decreased in all systems. The results suggest that use of NT systems under irrigated conditions will increase SOC sequestration, but rate of SOC accumulation will vary with cropping system.